1. Field of the Invention
This invention relates to utility knives usable for cutting cardboard, twine, plastic materials, thin wood, shrubbery, etc. More particularly, the invention relates to a protective guard structure for preventing injury to a person while holding a utility knife in his hand or storing such a knife in his pocket.
2. Prior Developments
Various types of guard structures for utility knives have been proposed. However such guard structures differ in material respects from the guard structure herein proposed. The herein-proposed guard structure is designed for use with a conventional utility knife, such that the guard structure can be supplied as an attachment to utility knife structures already in use; users of existing knife structures are enabled to purchase the guard structure without having to purchase a new knife.
A further feature of the herein-proposed guard structure is that it is automatically biased to the blade protective position when the person releases his grip on the knife handle. The person does not have to consciously think about moving the guard structure to its protective position, as movement to the protective position is automatic.
An additional advantage of the herein-proposed guard structure is that it is usable with knives having fixed cutter blades, i.e. knives wherein the cutter blade is rigidly mounted in the handle so as to be free from wobble or play when the knife is in use.
U.S. Pat. No. 4,086,698 to W. Sparks, shows one prior art knife construction having a guard that includes a shoe carried on a spring-biased plunger. The spring continually urges the shoe and plunger to the protective position. However the person can manipulate the knife so that the shoe presses against the work surface whereby the guard is retracted relative to the knife element, so that the knife element can penetrate the work. The guard operates in a different manner than the guard of the present invention.
J. Peyrot, U.S. Pat. No. 4,757,612, shows a utility knife having a fixed blade and a longitudinally slidable cover movable between a retracted position (FIG. 2), and an extended position overlying the fixed blade (FIG. 1). A manually-operated trigger is pivotably connected to the rear end of the handle to move the cover to its retracted position (by cam action). A major drawback of the Peyrot arrangement is its complexity and use of multiple moving parts. The manufacturing cost would also be relatively high.
U.S. Pat. No. 4,713,885, issued to R. Keklak, M. Couture and J. Whitehouse, shows a utility knife having a retractible cutter element (blade). The guard function is achieved by sliding the blade into the holder (handle) during non-use periods. The patented arrangement has a certain degree of complexity as regards the mechanism used to move the cutter blade out of the holder. As shown in FIG. 2 of the patent drawings, the mechanism includes a slide, pivotable links, a slideway for the link connector, and a squeezable lever. The mechanism is relatively complex.
J. Wood, U.S. Pat. No. 3,999,290, shows a utility knife wherein the cutter blade is slidable into and out of the handle (holder). In this respect the Wood patented device is similar to the devices shown in Peyrot U.S. Pat. No. 4,757,612 and Keklak et al U.S. Pat. No. 4,713,885, discussed above. In the Wood patented arrangement, the blade carrier is equipped with a wire spring arm having a hooked end, whereby the hooked end can catch on the cardboard work surface to draw the cutter blade out of the handle. The arrangement proposed by Wood is considerably different than what is proposed in the present invention.
U.S. Pat. No. 3,781,988, to R. Jones, discloses a utility knife having a guard swingable around a pivot between a retracted position (FIG. 2) and a use position (FIG. 1). An overcenter tension spring holds the guard in its two positions (retracted or extended). The guard is moved to its the retracted position when it is desired to change the cutter element. During normal operation the guard has its nose riding on the work surface to permit the blade to penetrate the work. The principal disadvantage of the patented arrangement would appear to be the cost of manufacture of the guard. The exposed location of spring S would also appear to be a disadvantage, in that the person's fingers could conceivably be pinched between the spring coils, under some circumstances.
Houghton et al, U.S. Pat. No. 4,028,802, shows a specialized yarn (loop) cutting tool having a swingable guard for the blade. The overall arrangement significantly differs from the arrangement of the present invention.
Vito, U.S. Pat. No. 4,531,286, shows a utility knife having a guard attached to the handle by a thin flexible wall. As best shown in FIG. 4, the flexible wall can flex to enable the blade to cut into the work surface. The patented arrangement differs considerably from the arrangement contemplated in the present invention.
Davis et al, U.S. Pat. No. 4,949,458, shows a utility knife having an extendable blade. The patentee states that if the handle is moved violently downwardly a latch member will be actuated to enable a guard (FIG. 4) to be projected out of the holder.
Chomiak, U.S. Pat. No. 5,241,750, shows a guard construction that includes a hood swingable between a protective position (FIG. 1) and a retracted position (FIG. 2). Springs normally hold the hood in its FIG. 1 position. A manual latch normally prevents dislocation of the hood from its FIG. 1 protective position.
The patents discussed above show various types of blade guards for use on utility knives. However, these patents do not show the specific guard structure proposed in the present invention.